Method of producing a solderable metallic coating on a ceramic body and of solderingto the coating



METHOD OF PRODUCING A SOLDERABLE METALLIC COATING ON A CERAMIC BODY AND OF SOLDERING TO THE CGATING Elma: Johannes Umblia, Hagersten, Sweden, assignor to Telefonaktiebolaget L M Ericsson, Stockholm, Sweden, a corporation of Sweden No Drawing. Application October 8, 1953 Serial No. 385,023

Claims priority, application Sweden November 5, 1952 8 Claims. (Cl. 29-4723) The present invention refers to a method for producing heat resistant soldered seams between metals and fireresistant, non-metallic materials (e. g. ceramics, quartz, graphites, carbides, etc.), or between two fire resistant, non-metallic materials. Such seams may be used in the production of diverse apparatuses and devices, where strong and heat-resistant connections between parts of the afore-mentioned materials must be obtained. Since furthermore such seams must be made vacuum tight and may not contain any glassy components, they are especially fit for use as connections for metal and ceramic details in electron-discharge and vacuum devices, which are to work at very high frequencies and/or high temperatures, and other electric devices.

In order that such a seam may be made by means of a hard solder, the non-metallic body must be provided with a particularly well adherent, solderable metallic coating. It is known that a well adherent metal coating on a nonmetallic body can be obtained by sintering onto the non-metallic seam surface a thin layer of molybdenum, tungsten or rhenium, possibly with addition of iron or manganese. The sintering operation is effected in an atmosphere of protective gas. In order that a strong connection be obtained between the sintered metal layer .and the non-metallic surface, especially ceramics, the furnace atmosphere must however absolutely comprise a determined, though very small quantity or oxygen. Owing thereto, there arises on the sintered surface of the metal tcoating an oxide film, which, however invisible, cannot, due to the great affinity of the said transition metals with oxygen, be removed even by a possible subsequent treatment with hydrogen gas at a temperature lower than the deformation temperature of most of the non-metallic materials in question, for example ceramics. Said oxide layer seams prevent the usual hard solders from flowing evenly over the sintered surface of the metal coating, said surface having therefore to be coated with a thin layer of some other easily deoxidizable and easily solderable metal, as nickel or copper. In order to obtain with certainty a strong and vacuum tight seam, said metal coating must before assembly be sintered onto the foundation coating in a reducing atmosphere. 1

The aforedescribed method for producing well solder- :able metallic coatings on non-metallic materials is thus characterized by the following two difficult moments: (I) the double metallizing or the non-metallic material, and (2) the necessity to regulate rather accurately the oxygen percentage of the protective gas.

The chief object of the present invention is to eliminate the over-metallizing of the metallic foundation coating without jeopardizing either its power of adhesion or its solderability.

A further object of the invention is to introduce the quantity of oxygen necessary for the fastening of the metal coating-to the non-metallic material in such a manner, that the protective gas is kept free from oxygen.

Another object of the invention to achieve, simul atent 2,835,967 Patented May 27, 1958 taneously with the metallizing of the non-metallic body, a hard solder seam between said body and the other pertaining metallic or non-metallic body.

It is a further and more special object of the invention to achieve a simplified method for vacuum tight hard soldering of metals and metallized ceramics, or of two metallized ceramic bodies, a method, which can advan tageously be applied in the production of electron-dis charge devices or other electric devices, where strong and heat-resistant, vacuum tight seams are to be achieved.

The principle of the invention for eliminating the double metallizing of the non-metallic material derives from the discovery that, if to molybdenum, tungsten, rhenium or some other refractory transition metal from the groups 4 to 6 of the periodical system, the characteristic property of which is, that under suitable sintering conditions they form a very strongly adherent but difficultly solderable metal layer on non-metallic materials, is added a suitable quantity of some easily deoxidizable and well solderable metal, as nickel or cobalt, a well adherent sinter layer is obtained, having such good soldering properties, that an over-metallizing of said layer is not necessary.

Another principle of the invention relating to the possibility of obtaining a well adherent metal coating by sintering also in an atmosphere of protective gas free from oxygen is based on thefact, that the small quantity of oxygen, which is required in order to produce a strong connection between the sintered metal layer and the ceramic, is added in the shape of a metal oxide, which is mingled with the metal powder to be sintered onto the ceramic. Said oxygen carrier suitably consists of an oxide of any of the metals constituting the foundation component of the sintered layer. In order not to consume unnecessarily the added oxygen, the sintering should suitably take place in a neutral atmosphere, and the subsequent cooling take place in a reducing atmosphere.

Though the invention is not going to be limited by any theory concerning its manner of action, it should be stated as an explanation that the improved soldering properties ofa metal coating achieved according to the invention seem to depend on the purposely added small quantity of oxygen, which has been evenly distributed in the powder layer, being unable to form any continuous oxide film on the surface of the coating, and this all the more as said coating, besides the difficultly oxidizable metal component, also comprises an easily deoxidizable component, which, even in case it were oxidized during the sintering process in neutral furnace atmosphere, is reduced again to metal at cooling in reducing furnace atmosphere. The condition that the atmosphere during sintering must be free from oxygen excludes the possibility of such considerable oxide films being formed, as can prevent a direct hard soldering on the coating.

The metallizing of non-metallic materials according to these principles is, in relation to the known methods, where owing to the difliculty of soldering the foundation coating said coating must be coated with a layer of another well solderable metal, both simpler and cheaper.

The procedure to produce the metal coating on a nonmetallic body is the following: on the well cleaned nonmetallic seam surface a thin layer of the component of the metal coating is applied in the shape of a fine-grain powder or a paste. According to the invention the powder mixture must have the following composition:

60-95 parts of a transition metal with high melting point from the groups 4 to 6 of the periodical system, for example molybdenum or tungsten, or rhenium,

0-5 parts iron,

5-40 parts ,preferably about 15 parts, of easily deoxidizable heavy metal, as nickel or cobalt,

tai'ning about nickel. 7 either in or above the scam in the shape of a metal sheet or wire or else be applied in the'shape of a paste. The

'0.051-0,5% preferably about'0.2%, oxides of any of the aforesaid metals, preferably nickel or cobalt oxides.

When the layer is to be applied in the form of a paste (or paint) a suspension means as lacquer, a solution of a plastic, vegetable oil, alcohol, water, etc., is added.

The non-metallic body coated with powder or paste is heated with a suitable speed to a temperature of 1200 to 1350 C. in an atmosphere of protective gas free from oxygen or in a vacuum and is kept at maximum temperature during -60 minutes to sinter the metal powder. The whole is thereafterco oled, preferably in areducing atmosphere;

Under certain circumstances it is also possible to achieve simultaneously both the metallizing'of the nonmetallic detail and the hard solderingv thereof to thef perraining metallic or non-metallic detail. 'The condition is that a hard solder with a melting point above 1200 7C.

beuse d, for example an alloy of copper and nickel con- The solder may be fixed whole must thereafter be heated up to a temperature lying about C. higher than the melting point of the'solder.

The heating must take place in an atmosphere'free from oxygen or in a vacuum. e

,It. is obvious that, besides the aforesaid modifications, different other changes and modifications may also be f fmade without the principle of the invention being 'depa'rted from. r a

Iclaim: f Q, J a V '1; The method which comprises applying to the surface of a ceramic member a layer of a powdered mixture,

consisting essentially of -95 percent ofv a refractory metal selected from the class consisting of molybdenum, tungstenandrhenium, 5-40 percent of an easily deoxizable metal selected from the class consisting of nickel and 'cobalt and 005-05 percent of an oxide of armetal of the aforesaid classes, heating said member and layer to a temperature of .l200,l350,"C.' for 30-60 minutes in an inert atmosphereito sinter said powders, and then cooling 7 after s'inten'ng in a reducing atmosphere;

2. Process in accordance 'withclaim 1 wherein the powdered mixture. includesii'r'on in an amount up to 5 percent.

Said suspensionis applied by means of painting or i spr'ayingl i 3. A powdered mixture consisting essentially of '60 percent of a refractory metallselected from, the. class.

consisting of molybdenum, tungsten and rhenium, 54() percent of an easily deoxizable metal selected from the class consisting of nickel'and cobalt and 0.050.5 percent e of an oxide of a metal ofthe aforesaid classes.

LA powdered mixture in accordance WithcIaim 3 which includes iron in an amount up to 5 percent;

5. Method ofbonding-a solderable element to aceramic body Whic'hcomprises metallizing the surface of" the ceramic body by the method of claim 1, and soldering said element and said metallized surface.

6. Method of bonding a solderable element to a ceramic body which comprises metallizing the surface of the j 2 ceramic body by the method of. claim 2, and soldering said element and said metallized surface. s V i 7. Method of bonding ceramic bodies which comprises metallizing a surface of eachof said ceramic bodies by the method of claim 1, and soldering said'metallized surfaces.

V 8-, Me h d of d ng ce mic o i wh ch comp metallizing a surface of each of said ceramic bodies by the method of claim 2, and soldering'said metallized= surfaces.

' 7 References Cited in thetfile of this patent UNITED STATES'PATENTS r OTHER REFERENCES 7 ,7 Glass to Metal Seals by]. H. Partridge, pages 81 and 82. Published by The Society of Glass Technology,

Shefiield, England in 1949. (Copy in. Divisionl4.) 

1. THE METHOD WHICH COMPRISES APPLYING TO THE SURFACE OF THE CERAMIC MEMBER A LAYER OF A POWDERED MIXTURE CONSISTING ESSENTIALLY OF 60-95 PERCENT OF A REFRACTORY METAL SELECTED FROM THE CLASS CONSISTING OF MOLYBDENUM, TUNGSTEN AND RHENIUM, 5-40 PERCENT OF AN EASILY DEOXIZABLE METAL SELECTED FROM THE CLASS CONSISTING OF NICKEL AND COBALT AND 0.05-0.5 PERCENT OF AN OXIDE OF A METAL OF THE AFORESAID CLASSES, HEATING SAID MEMBER AND LAYER TO A TEMPERATURE OF 1200-1350*C. FOR 30-60 MINUTES IN AN INERT ATMOSPHERE TO SINTER SAID POWDERS, AND THEN COOLING AFTER SINTERING IN A REDUCING ATMOSPHERE.
 5. METHOD OF BONDING A SOLDERABLE ELEMENT OF A CERAMIC BODY WHICH COMPRISES METALIZING THE SURFACE OF THE CERAMIC BODY BY THE METHOD OF CLAIM 1, AND SOLDERING SAID ELEMENT AND SAID METALLIZED SURFACE. 